It depends on why you are bringing the dehydrated entree in the first place. If it's just some comfort food then I guess 1/2 of a package might work.
Consider though that most Mountain House entrees are about 300 calories per official serving. Mary Janes Farm packages about 500 calories per "1.5 serving" package with the intent that it really is meant for one person.
I find that 500-600 calories is a good amount for a dinner entree. Less and is doesn't have enough calories to bother with, more and it can be hard to get down if I'm tired. I supplement the entree with things like pudding, cocoa, leftover lunch items, candy, and/or a steam baked muffin to bring the meal up to about 1,000 calories.
That's in the context of a 2500 to 3000 calorie day. If you need more total then maybe a bigger entree would be in order.